Severe Storm Outlook Narrative (AC)
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Issued by NWS
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330 ACUS01 KWNS 051624 SWODY1 SPC AC 051622 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1122 AM CDT Wed Jun 05 2024 Valid 051630Z - 061200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE UPPER MIDWEST...GREAT LAKES...NORTHEAST...MID-ATLANTIC...SOUTHERN TEXAS...AND SOUTHERN MISSISSIPPI... ...SUMMARY... Strong storms are possible across portions of the Upper Midwest, Great Lakes, Northeast, Mid-Atlantic, parts of southern and coastal Texas, and southern Mississippi. ...Synopsis... Water-vapor imagery shows a mid-level shortwave trough over the western Great Lakes/mid MS Valley with the primary vorticity lobe rotating northeastward through the Upper Great Lakes through the early evening. A blocking pattern located over the Northeast into Quebec will weaken as a mid-level speed max moves quickly from the western Dakotas southeastward into the southern Great Lakes by early Thursday morning. In the low levels, a cold front will arc southeastward into the Great Lakes from an occluded low over Manitoba/western Ontario. The trailing portion of the front will progress eastward across the southern Great Lakes/OH Valley, while the convectively augmented effective front stalls over the northwest Gulf Coast states. ...MN/WI to the Mid-Atlantic this afternoon/evening... Surface heating and lingering boundary-layer moisture will contribute to weak-moderate buoyancy in an environment with sufficient westerly deep-layer shear/hodograph length for scattered, low-topped cells to produce isolated severe gusts and marginally severe hail this afternoon across MN/WI. Farther southeast over the southern Great Lakes/OH Valley, ascent associated with the aforementioned Great Lakes mid-level disturbance will aid in storm development this afternoon as heating weakens convective inhibition. Relatively moist low levels (surface dewpoints 65-70 deg F) will contribute to MLCAPE around 1000 J/kg. Moderate deep-layer vertical shear (effective bulk shear 20-30 kt) along with poor midlevel lapse rates around 6 C/km, will favor mostly strong to locally severe multicells. Isolated 50-65 mph gusts and marginally severe hail are the primary hazards. Remnant, convectively enhanced midlevel troughs will move east-northeastward from WV and AL, coincident with the diurnal heating cycle near and east of the Appalachians. Widely scattered storm clusters will be possible this afternoon from GA into the western Carolinas, but poor lapse rates and weak vertical shear will limit any severe threat. Though lapse rates will be similarly poor into the Mid-Atlantic, there will be a zone of stronger low-level shear/hodograph curvature across northern VA/MD in advance of the MCV approaching from WV. Here, a few weakly rotating storms could produce isolated wind damage and a brief/weak tornado. ...TX/LA/MS... Remnant MCS will continue to push southward through the middle TX coast through early afternoon and offshore the southwest LA coast. Several observation sites late this morning recorded strong gusts (40-45 kt) but the overall displacement of the gust front from the thunderstorm cores will likely limit gust potential. A few storms may develop farther west this afternoon/evening along the trailing outflow boundary in the area around DRT. Large CAPE/steep lapse rates will support both strong updrafts and downdrafts, though weak vertical shear will generally limit storm longevity and the magnitude of any hail/wind threat. Farther east over LA/MS, scattered thunderstorms are forecast to develop near the residual outflow. An isolated hail/wind threat may develop with the stronger storms as one or two clusters develops by mid-late afternoon and early evening. ...ME/NH this afternoon... Downstream of shortwave ridging in the midlevels, a weak northwest flow regime will persist this afternoon over northern New England. Lingering low-level moisture, surface heating in cloud breaks southeast of the higher terrain, and very subtle midlevel vorticity maxima will support a few thunderstorms this afternoon across southern/eastern ME and part of NH. The latest forecast soundings show MLCAPE of 1000-1500 J/kg and effective bulk shear near 25 kt (with longer hodographs aloft) will be sufficient for semi-organized storms capable of producing isolated wind damage and marginally severe hail for a few hours this afternoon. ..Smith/Hart.. 06/05/2024 $$